Refractive scanning interferometer

Abstract

Embodiments are disclosed relating to a refractively-scanning interferometer comprising an aperture that receives an incident light beam at a receiving angle, a beam splitter configured to split the incident light beam into a first beam and a second beam, a first and a second reflector arranged to reflect the first beam and second beam, respectively, towards a combining optical element, and a refractive Optical Path Difference (rOPD) assembly interposed between the beam splitter and the first reflector, wherein the rOPD Assembly refracts the first light beam an even number of times with induced phase discrepancy being a vector sum of a first phase discrepancy induced by a first refraction and a second phase discrepancy induced by a second refraction, the rOPD Assembly being configured such that the first phase discrepancy is substantially opposite in direction to the second phase discrepancy, a portion of the first and second phase discrepancies cancelling one another out to decrease magnitude of the phase discrepancy.

The invention claimed is: 
     
       1. A scanning interferometric system comprising:
 an aperture that receives an incident light beam at a receiving angle; 
 a beam splitter configured to split the incident light beam into a first beam and a second beam; 
 a first and a second reflector arranged to reflect the first beam and second beam, respectively, towards a combining optical element; and 
 a refractive Optical Path Difference (rOPD) assembly interposed between the beam splitter and the first reflector; 
 wherein the rOPD Assembly comprises at least one pivotable refractor able to pivot about an axis extending substantially perpendicular to an optical Z axis of the first beam, said optical Z axis being an ideal direction of travel of the first beam; 
 said at least one pivotable refractor being arranged to refract the first beam, thereby inducing a difference in path length between the first and second beams, thereby phase-shifting the first beam relative to the second beam; and 
 the combining optical element is configured to receive and combine the phase-shifted first beam and the second beam into an output beam having an interference pattern induced by the phase-shifted first beam and the second beam interfering with one another; 
 further wherein the interference pattern contains a phase discrepancy induced during refraction of the first light beam and having a magnitude dependent upon the receiving angle; 
 the aperture has a critical receiving angle, being a maximum value of the receiving angle, beyond which the induced phase discrepancy is of sufficient magnitude to render a produced interference pattern illegible, invisible or otherwise undetectable; 
 the rOPD assembly is arranged to refract the first beam by the at least one pivotable refractor an even number of times as it passes therethrough, said even number comprising an equal number of first refractions and second refractions, said first refractions being refractions along the optical X axis, said second refractions being refractions along the optical Y axis, and said optical X & Y axes being optically perpendicular to one another and to the optical Z axis of the first beam; 
 the phase discrepancy is a vector sum of a first phase discrepancy induced by a first refraction and a second phase discrepancy induced by a second refraction; and 
 the rOPD Assembly is configured such that the first phase discrepancy is substantially opposite in direction to the second phase discrepancy, such that a portion of the first and second phase discrepancies cancel one another out, thereby decreasing magnitude of the phase discrepancy. 
 
     
     
       2. The system of  claim 1 , wherein the at least one pivotable refractor is a single pivotable refractor that refracts the first light beam for the even number of times, the single pivotable refractor adapted to refract the first light beam along the optical X or Y axis thereof; and
 The rOPD Assembly further comprises a light-rotating element arranged to rotate the first light beam by approximately 90° about the optical Z axis between successive refractions, thereby flipping the optical X and Y axes of the first light beam, such that the successive refractions alternate between being first and second refractions. 
 
     
     
       3. The system of  claim 2  wherein the rOPD is further arranged to direct the first light beam through the light-rotating element an even number of times between successive refractions, each time rotating by approximately 45°. 
     
     
       4. The system of  claim 2 , wherein both the first beam and the second beam are refracted an even number of times by the rOPD Assembly;
 the second beam has a further optical Z axis, said further optical Z axis being an ideal direction of travel of the second beam; 
 the single pivotable refractor of the rOPD Assembly is a dual-beam pivotable retractor that is configured to refract each of the first and second beams an even number of times, the dual-beam pivotable retractor having a pivot axis perpendicular to the optical Z axis and the further optical Z axis; and 
 the light-rotating element is configured to rotate the first light beam by approximately 90° about the optical Z axis and the second light beam by approximately 90° about the further optical Z axis. 
 
     
     
       5. The system of  claim 4 , wherein the light-rotating element comprises:
 a first light-rotating element arranged to rotate the first light beam by approximately 90° about the optical Z axis; and 
 a second light-rotating element arranged to rotate the second light beam by approximately 90° about the further optical Z axis. 
 
     
     
       6. The system of  claim 2 , wherein both the first beam and the second beam are refracted an even number of times by the rOPD Assembly;
 the system further comprises a second pivotable retractor arranged to refract the second light beam; and 
 the light-rotating element is configured to rotate the first light beam by approximately 90° about the optical Z axis and the second light beam by approximately 90° about the further optical Z axis. 
 
     
     
       7. The system of  claim 6 , wherein the light-rotating element comprises:
 a first light-rotating element arranged to rotate the first light beam by approximately 90° about the optical Z axis; and 
 a second light-rotating element arranged to rotate the second light beam by approximately 90° about the further optical Z axis. 
 
     
     
       8. The system of  claim 1 , wherein the at least one pivotable refractor comprises:
 an X-axis pivotable refractor that induces the first refractions in the first beam; and 
 a Y-axis pivotable refractor that induces the second refractions in the first beam. 
 
     
     
       9. The system of  claim 8 , wherein the X-axis pivotable refractor and y-axis pivotable refractor have pivot axes that are not physically perpendicular to one another; and
 the rOPD Assembly further comprises a light-rotating element between the X-axis pivotable refractor and y-axis pivotable refractor that is arranged to rotate the first beam about the optical Z axis, such that the X-axis pivotable refractor and y-axis pivotable refractor are optically perpendicular to one another. 
 
     
     
       10. The system of  claim 8 , wherein both the first beam and the second beam are refracted an even number of times by the rOPD Assembly, and at least one of the X-axis pivotable refractor and Y-axis pivotable refractor is a dual-beam pivotable refractor that is configured to refract both the first beam and the second beam. 
     
     
       11. The system of  claim 8 , wherein both the first beam and the second beam are refracted an even number of times by the rOPD Assembly, and wherein either:
 the X-axis pivotable refractor comprises a first X-axis pivotable refractor positioned to refract the first beam, and a second X-axis pivotable refractor positioned to refract the second beam; 
 the Y-axis pivotable refractor comprises a first Y-axis pivotable refractor positioned to refract the first beam, and a second Y-axis pivotable refractor positioned to refract the second beam; or 
 the X-axis pivotable refractor comprises a first and second X-axis pivotable refractor, and the Y-axis pivotable refractor comprises a first and second Y-axis pivotable refractor. 
 
     
     
       12. The system of  claim 1 , wherein both the first beam and the second beam are refracted an even number of times by the rOPD Assembly. 
     
     
       13. The system of  claim 1 , wherein the combining optical element is the beam splitter, such that the system is a Michelson-type interferometric system.